Low noise pneumatic tire

ABSTRACT

This invention provides a low noise pneumatic tire allowed to achieve an efficient noise reduction effect by making full use of characteristics of a sound absorbing material. A pneumatic tire according to the present invention is a low noise pneumatic tire where a band-shaped sound absorbing material formed of a porous material whose apparent density defined in JIS K6400 is in a range of 10 to 70 kg/m 3 , is attached on the inner surface of a tread by use of an elastic fixing band.

TECHNICAL FIELD

The present invention relates to a low noise pneumatic tire, and morespecifically, relates to a low noise pneumatic tire allowed toeffectively reduce noise caused by cavity resonance.

BACKGROUND ART

One of the causes of tire noise is cavity resonance sound caused byvibration of air filled in the inside of a tire. When the tire isrotated under a load, a ground-contacting portion in a tread portion ofthe tire vibrates because of irregularities on a ground surface and thisvibration causes vibration of the air inside the tire and generates thecavity resonance sound. This cavity resonance sound is generated byvibration of air inside the tire caused by vibration of aground-contacting portion in a tread portion of the tire which isgenerated by irregularities on a ground surface when the tire is rotatedunder a load. In this cavity resonance sound, it has been known thatfrequencies perceived as noise are approximately 200 to 250 Hz althoughthey differ by tire size. Therefore, for the purpose of reducing tirenoise, it is important to reduce noise level in a range of the abovefrequencies.

As a method of reducing noise caused by the cavity resonance phenomenonas above, there has been a proposed approach where a sound-absorbingmaterial is added to the inside of a tire to absorb resonance (refer toPatent Document 1, for example). However, a full consideration has notbeen given to characteristics of the sound-absorbing material in thisapproach, and it is not necessarily considered that the approach hasachieved an excellent result in noise reduction. [Patent Document 1]Japanese patent application Kokai publication No. Sho62-216803

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a low noise pneumatictire allowed to achieve an efficient noise reduction effect by makingfull use of characteristics of a sound absorbing material.

A pneumatic tire according to the present invention for achieving theabove object is formed of any one of the following (1) to (11):

(1) A low noise pneumatic tire, where a band-shaped sound absorbingmaterial formed of a porous material whose apparent density defined inJIS K6400 is in a range of 10 to 70 kg/m³, is attached to the innersurface of a tread by use of an elastic fixing band;

(2) The low noise pneumatic tire according to (1), where the band-shapedsound absorbing material is fixed all around the entire circumference onthe inner surface of the tread by use of an elastic fixing band;

(3) The low noise pneumatic tire according to any one of (1) and (2),where an irregular surface having step heights equal to or less than 20mm is formed on the inner peripheral surface of the band-shaped soundabsorbing material;

(4) The low noise pneumatic tire according to any one of (1) to (3),where a second porous material whose sound absorption coefficientdefined in JIS A1405 at a frequency of 200 Hz is at least 10%, islayered on a cavity-facing surface of the band-shaped sound absorbingmaterial;

(5) The low noise pneumatic tire according to (4), where the band-shapedsound absorbing material has a thickness in a range of 5 to 45 mm, andthe second porous material has a flat surface and has a thickness in arange of 5 to 45 mm;

(6) The low noise pneumatic tire according to (4), where irregularitieshaving step heights equal to or less than 20 mm are formed on a surfaceof the second porous material;

(7) The low noise pneumatic tire according to (6), where the band-shapedsound absorbing material has a thickness in a range of 5 to 45 mm, andthe second porous material has a thickness in a range of 5 to 45 mm;

(8) The low noise pneumatic tire according to any one of (1) to (3),where a porous material whose sound absorption coefficient defined inJIS A1405 at a frequency of 200 Hz is at least 10%, is layered on bothinner and outer surfaces of the band-shaped sound absorbing material;

(9) The low noise pneumatic tire according to any one of (1) to (8),where the elastic fixing band has a stretching mechanism, whichautomatically adjusts a circumferential length of the elastic fixingband, in at least one location on the circumference of the elasticfixing band;

(10) The low noise pneumatic tire according to (9), where the stretchingmechanism is formed of an elastic spring mechanism; and

(11) The low noise pneumatic tire according to (9), where the stretchingmechanism is formed by coupling both ends of the elastic fixing bandwith each other in a manner that the elastic fixing band can slide.

According to a low noise pneumatic tire of the present invention, byforming a band-shaped sound absorbing material from a porous materialand appropriately setting the apparent density defined in JIS K6400 forthe porous material, and by attaching the porous material all around anentire circumference on an inner surface of a tread of the tire by useof an elastic fixing band, an effect of reducing tire cavity resonancesound is obtained through a sound absorption function realized allaround the circumference by the porous material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a low noise pneumatic tireaccording to an embodiment of the present invention, taken along ameridian of the tire, when the tire is assembled with a rim and isinflated with a pneumatic pressure.

FIG. 2 a is a side view for explaining an arrangement relation between aband-shaped sound absorbing material and an elastic fixing bandaccording to the embodiment of the present invention.

FIG. 2 b is another side view for explaining another arrangementrelation between the band-shaped sound absorbing material and theelastic fixing band according to the embodiment of the presentinvention.

FIG. 3 a is a perspective view for explaining a superficial shape of aninner circumferential surface of the band-shaped sound absorbingmaterial according to the embodiment of the present invention.

FIG. 3 b is a perspective view for explaining a superficial shape of aninner circumferential surface of another band-shaped sound absorbingmaterial according to the embodiment of the present invention.

FIG. 3 c is a perspective view for explaining a superficial shape of aninner circumferential surface of still another band-shaped soundabsorbing material according to the embodiment of the present invention.

FIG. 3 d is a perspective view for explaining a superficial shape of aninner circumferential surface of still another band-shaped soundabsorbing material according to the embodiment of the present invention.

FIG. 3 e is a perspective view for explaining a superficial shape of aninner circumferential surface of still another band-shaped soundabsorbing material according to the embodiment of the present invention.

FIG. 4 a is a side view for explaining a layered structure of a soundabsorbing material according to the embodiment of the present invention.

FIG. 4 b is a side view for explaining another layered structure of thesound absorbing material according to the embodiment of the presentinvention.

FIG. 5 a is a side view for explaining a layered structure of a soundabsorbing material according to one other embodiment of the presentinvention.

FIG. 5 b is a side view for explaining another layered structure of thesound absorbing material according to the one other embodiment of thepresent invention.

FIG. 6 a is a perspective view for explaining an arrangement of theelastic fixing band according to the embodiment of the presentinvention.

FIG. 6 b is a perspective view for explaining another arrangement of theelastic fixing band according to the embodiment of the presentinvention.

FIG. 6 c is a perspective view for explaining another arrangement of theelastic fixing band according to the embodiment of the presentinvention.

FIG. 7 is a side view showing a low noise pneumatic tire according toone example of the present invention, using an elastic fixing bandprovided, in at least one location on the circumference of the elasticfixing band, with the stretching mechanism which automatically adjusts acircumferential length of the elastic fixing band.

FIG. 8 is a cross-sectional view showing the tire in a state where it isfully inflated with a pneumatic pressure, taken along a meridian of thetire, for explaining the main portion of the example shown in FIG. 7 ofthe present invention.

FIG. 9 a is a schematic view showing one example of the stretchingmechanism used in the elastic fixing band shown in FIG. 7 according toone aspect of the present invention.

FIG. 9 b is a schematic view showing another example of the stretchingmechanism used in the elastic fixing band shown in FIG. 7 according toone aspect of the present invention.

FIG. 10 is a schematic view showing still another example of thestretching mechanism used in the elastic fixing band shown in FIG. 7according to one aspect of the present invention.

FIG. 11 is an illustration for explaining a buckling phenomenon of atire.

EXPLANATION OF NUMERALS AND SYMBOLS

-   -   1: tread portion    -   2: bead portion    -   3: sidewall portion    -   4: cavity portion    -   5: band-shaped sound absorbing material    -   5 a: second porous material    -   6: elastic fixing band    -   7 a, 7 b and 7 c: plate spring    -   7: coupling jig    -   G: ground surface    -   Q: ground-contacting portion

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, detailed descriptions will be given of configurations ofthe present invention with reference to the attached drawings.Components common among any plural drawings thereof are attached withthe same numerals and symbols, so that duplicated descriptions areomitted.

FIG. 1 is a cross-sectional view showing one example of a low noisepneumatic tire of the present invention, taken along a meridian of thetire. FIGS. 2 a and 2 b are side views showing two different examplesfor explaining the main portion of the tire in FIG. 1. In FIG. 1, a lownoise pneumatic tire T includes: a tread portion 1; a pair of left andright bead portions 2; a sidewall portion coupling the tread portion 1to the bead portions 2. When the tire T is mounted on a rim R, a cavityportion 4 is formed between the tire T and the rim R.

On an inner surface of the tread portion 1, as shown in FIGS. 2 a and 2b, a band-shaped sound absorbing material 5 is attached all around anentire circumference of the inner surface of the tread portion by use ofan elastic fixing band 6 in a manner that the band-shaped soundabsorbing material is attached by pressure to the inner surface of thetread portion 1 by utilizing elasticity of the elastic fixing band. Theband-shaped sound absorbing material 5 is formed of a porous materialwhose apparent density defined in JIS K6400 is in a range from 10 to 70kg/m³, and the elastic fixing band 6 is formed of a synthetic resinhaving a high tensile modulus. Note that both ends of the elastic fixingband 6 in a longitudinal direction thereof are coupled with each otherin a manner that a circumferential length thereof can be changed.

Although, in FIGS. 2 a and 2 b, examples where the band-shaped soundabsorbing material 5 is attached all around an entire circumference ofthe inner surface of the tread portion by use of an elastic fixing band6, the band-shaped sound absorbing material does not always have to bepresent around the entire circumference thereof. Based on variousknowledge of inventors of the present invention, the band-shaped soundabsorbing material may be attached around at least 75% of the entirecircumferential length of the inner surface of the tread portion, morepreferably at least 80% of the entire circumferential length thereof,and most preferably at least 90% of the entire circumferential lengththereof. Based on knowledge of the inventors, the case where theband-shaped sound absorbing material is attached all around entirecircumference on inner surface of the tread portion is most effectiveand most preferable.

In FIG. 1, an example where the band-shaped sound absorbing material 5is attached in a manner that it is attached from the inner circumferenceby pressure to the inner surface of the tread portion 1 by use of theelastic fixing band 6 is shown. However, a positional relation betweenthe band-shaped sound absorbing material 5 and the elastic fixing band 6in the tire radial direction may be such that the elastic fixing band 6is arranged to an outer circumference of the band-shaped sound absorbingmaterial 5. In any one of the above configurations, it is only necessaryfor the elastic fixing band 6 to attach the band-shaped sound absorbingmaterial 5 to the inner surface of the tread portion 1 by pressure byfixing the band-shaped sound absorbing material 5 by use of a bond orthe like and coupling the both ends of the band-shaped sound absorbingmaterial 5 in the lengthwise direction thereof with each other.

Thus, by having an apparent density thereof defined in JIS K6400 to be70 kg/m³ or less, even while having a porous structure, the band-shapedsound absorbing material 5 can maintain a structure in such a mannerthat the structure does not suffer compressive deformation due to aninner pressure of the tire. Consequently, a high sound absorption effectcan be obtained. However, if the apparent density thereof is lower than10 kg/m³, a sound absorption performance cannot be obtained because ofthe excessive size of a porous structure thereof.

Thus, the density of the band-shaped sound absorbing material 5 is setwithin a specific range, and consequently, while having a porousstructure, the band-shaped sound absorbing material 5 does not suffercompressive deformation due to an inner pressure of the tire. Therefore,an excellent sound absorption effect can be obtained. Additionally, theband-shaped sound absorbing material 5 is attached by pressurepreferably around at least 75% of the circumferential length of theinner surface of the tire, or more preferably, all around the entirecircumference of the inner surface of the tire, by use of elasticity ofthe elastic fixing band 6 as described above, and hence, is maintainedin a stable state where the band-shaped sound absorbing material is hardto separate.

As the porous material forming the band-shaped sound absorbing material5, resin foam is preferable, and low density polyurethane foam isparticularly preferable because it has resistance such that it suffersless compressive deformation due to the inner pressure of the tire. Aconfiguration of bubbles is preferably continuous. Additionally, as theporous material, other than resin foam, non-woven fabric such as felt ormat formed by bonding fibers may be used.

As a material forming the elastic fixing band 6, synthetic resin such aspolypropylene resin is preferably used, and in a case wherepolypropylene resin is used, the polypropylene resin having a flexuralmodulus in a range of 1100 to 1800 MPa is preferably used. If theflexural modulus thereof is less than 1100 MPa, elasticity thereof is sosmall that it becomes more difficult for the elastic fixing band 6 tofully exert functions as an elastic band. If the flexural modulusthereof exceeds 1800 MPa, stiffness thereof is so high that the elasticfixing band 6 cannot follow deformation at the time when a tire contactsthe ground and thereby become more breakable and durability thereof isreduced. More preferably, the flexural modulus thereof may be set withina range of 1300 to 1700 MPa. Note that the flexural modulus describedhere is a value obtained by a method of testing a flexural modulusdefined in ASTM (American Society for Testing and Material) D790.

In the embodiment shown in FIG. 2 a, a case is shown where theband-shaped sound absorbing material 5 is attached on the inner surfaceof the tread portion 1 in a manner that it is attached thereto bypressure by use of an elastic fixing band 6 placed to the inner surfaceof the band-shaped sound absorbing material 5. However, with respect toa positional relation in a radial direction of the tire between theelastic fixing band 6 and the band-shaped sound absorbing material 5,the elastic fixing band 6 may be placed to an outer surface of theband-shaped sound absorbing material 5 as shown in FIG. 2 b. In bothembodiments, it is only necessary for the elastic fixing band 6 toattach the band-shaped sound absorbing material 5 by pressure to theinner surface of the tread portion 1 by fixing the band-shaped soundabsorbing material 5 by use of a bond or the like and coupling the bothends of the band-shaped sound absorbing material 5 in the lengthwisedirection thereof with each other.

Additionally, on the inner peripheral surface of the band-shaped soundabsorbing material 5, it is better to form irregularities in order toenhance a sound absorbing effect. Although the shape of the irregularsurface is not particularly limited, any one of shapes shown in FIGS. 3a to 3 e is applicable. It is better to set a step height of theirregularities on this irregular surface to 20 mm or less.

In the present invention, it is more preferable to layer a second porousmaterial with a different sound absorption characteristic from that ofthe foregoing porous material, on a surface of the band-shaped soundabsorbing material 5 facing the cavity portion 4. In such a case asabove where another porous material is layered on one porous material,as shown in FIGS. 4 a and 4 b as examples, it is preferable that, whilethe one porous material is arranged facing the inner surface of thetire, the second porous material 5 a whose sound absorption coefficientdefined in JIS A1405 at a frequency of 200 Hz is at least 10%, islayered on a surface thereof facing the cavity portion 4. By having anapparent density of 10 to 70 kg/m³, the one porous material is excellentenough in resistance to compression not to be crushed by a pneumaticpressure inside the cavity portion 4. Still in this case, it is betterto form irregularities on a surface of the second porous material 5 a.The second porous material 5 a may be resin foam or may be non-wovenfabric or the like.

Note that the sound absorption coefficient described in the presentinvention is a sound absorption coefficient defined in JIS A1405.

In the case as described above where a layered body is formed with theband-shaped sound absorbing material 5 and the second porous material 5a, a thickness A of the band-shaped sound absorbing material 5 is set ina range of 5 to 45 mm. A thickness B of the second porous material 5 ais set preferably in a range of 5 to 45 mm, and more preferably in arange of 5 to 10 mm, in a case where the second porous material 5 a hasa flat surface as shown in FIG. 4 a, and is set preferably in a range of5 to 45 mm, and more preferably in a range of 5 to 20 mm, in a casewhere the second porous material 5 a has an irregular surface as shownin FIG. 4 b. Thereby, a crush of the band-shaped sound absorbingmaterial 5 due to the internal pressure of the tire and loss of thesound absorption effect are prevented, and also, a sound absorptionperformance can be enhanced. It is better to set a thickness of thelayered body formed with the band-shaped sound absorbing material 5 andthe second porous material 5 a to 50 mm or less.

In the case as described above where the second porous material 5 a islayered on the surface of the band-shaped sound absorbing material 5, itis better to form a large number of holes S in the second porousmaterial 5 a for the purpose of further enhancing the sound absorptioneffect. The holes S lead to the band-shaped sound absorbing material 5which is excellent in resistance to compression. Thereby, the holes Sperform a role as a passage through which an acoustic energy from thecavity portion 4 of the tire is taken into the band-shaped soundabsorbing material 5, and also can prevent a crush of the band-shapedsound absorbing material 5 due to the pneumatic pressure of the tire.

Furthermore, as shown in FIG. 5 b, it is also possible to have astructure where both inner and outer surfaces of the band-shaped soundabsorbing material 5, which is excellent in resistance to compression,are covered with the second porous material 5 a. Thereby, the secondporous material 5 a is arranged to contact the inner surface of the tirewhich is a source of cavity resonance, whereby the sound absorptioneffect is increased from that in the case where the second porousmaterial 5 a is arranged only on the inner surface of the band-shapedsound absorbing material 5.

Note that, with respect to a positional relation in a radial directionof the tire between the band-shaped sound absorbing material 5 and theelastic fixing band 6 in the case where the second porous material 5 ais layered on a surface of the band-shaped sound absorbing material 5,the elastic fixing band 6 may be placed to the inner periphery or to theouter periphery of the band-shaped sound absorbing material 5 as shownin FIG. 6 a or 6 c, and furthermore, may be placed between theband-shaped sound absorbing material 5 and the second porous material 5a as shown in FIG. 6 b.

The band-shaped sound absorbing material 5 and the elastic fixing band 6according to the present invention are attached onto the tire T after ithas gone through a vulcanization process, and for this reason, thisinvention does not necessitate alteration of production facilities andthe like and is applicable to existing tires.

Note that, particularly by allowing the circumferential length of theelastic fixing band 6 to be variable and adjusting the circumferentiallength of the band-shaped sound absorbing material 5, it becomespossible to apply the common band-shaped sound absorbing material 5 andelastic fixing band 6 to various kinds of pneumatic tires. Furthermore,the band-shaped sound absorbing material 5 and the elastic fixing band 6described above cannot be an obstacle against workability at the time oftire-rim assembly because they can be attached all around the entirecircumference on the inner surface of the tread portion 1 of the tire T.

Particularly in order to allow the circumferential length of the elasticfixing band 6 to be variable and to make it possible to adjust thecircumferential length of the band-shaped sound absorbing material 5 asdescribed above, it is preferable to use an elastic fixing band providedwith a stretching mechanism, which automatically adjusts thecircumferential length of the elastic fixing band, in at least onelocation on a circumference of the elastic fixing band.

In an illustration of an example of the above elastic fixing band shownin FIG. 7, the elastic fixing band 6 is preferably formed of a metal.The entirety of the elastic fixing band 6 is formed in a manner that thecircumferential length thereof is cut off in at least one location (fourlocations in the illustration) on the circumference and both ends of aspace thus cut off are coupled by a plate spring 7 a which is bent in aU-shape. A portion corresponding to this U-shaped plate spring 7 a ismeant to work as a stretching mechanism which automatically absorbs acomponent in the circumferential direction of a load applied to theelastic fixing band 6. FIG. 8 is a cross-sectional view showing a statewhere a low noise pneumatic tire of the example shown in FIG. 7 is fullyinflated with a pneumatic pressure, and the view is taken along ameridian of the tire. In the example shown in FIGS. 7 and 8, the elasticfixing band is arranged to the outer periphery of the band-shaped soundabsorbing material 5 as shown in FIG. 2 b.

As this kind of a stretching mechanism formed of the plate spring 7 a, aplate spring 7 b or 7 c which is bent in a zig-zag manner as shown inFIG. 9 a or 9 b as an example may be used. Note that, although a numberof the stretching mechanisms formed on the circumference of the elasticfixing band 6 is not particularly limited, it is better to arrange thestretching mechanisms evenly in three to eight locations on thecircumference.

With respect to a width of the elastic fixing band 6, it is preferableto set the width in a range of 10 to 30 mm, and the width may beappropriately decided according to stiffness of the band-shaped soundabsorbing material 5 within this range. If the width of the elasticfixing band 6 is less than 10 mm, strength of the elastic fixing band isinsufficient. If the width of the elastic fixing band 6 exceeds 30 mm,it is not preferable because a weight of the elastic fixing bandincreases. With respect to a thickness of the elastic fixing band 6, itis preferable to set the thickness in a range of 0.5 to 2.0 mm. If thethickness of the elastic fixing band 6 is less than 0.5 mm, strength ofthe elastic fixing band is insufficient. If the thickness of the elasticfixing band 6 exceeds 2.0 mm, it is not preferable because the elasticfixing band becomes more breakable due to excessive flexural stiffness.It is more preferable to set the thickness of the elastic fixing band ina range of 0.75 to 1.5 mm.

In a tire where the elastic fixing band 6 is provided with thestretching mechanism 7 a, 7 b or 7 c, even when an external force whichmay generate a buckling phenomenon or the like acts upon the elasticfixing band 6, the stretching mechanism automatically absorbs theexternal force. Consequently, a life of the elastic fixing band 6 can beprolonged, and additionally, attachment of the band-shaped soundabsorbing material 5 to the inner surface of the tread can bestabilized.

FIG. 10 shows still another example of the stretching mechanism. Bothends 6 b, 6 c of the elastic fixing band 6 in a lengthwise directionthereof are coupled with each other by use of a coupling jig in a mannerthat the elastic fixing band can slide. That is, while one end 6 b ofthe elastic fixing band 6 is fixed to the coupling FIG. 7, the other end6 c thereof is allowed to freely slide to the directions indicated byarrows. For the purpose of securing a smooth slide of the end 6 c, it isbetter to cover the end 6 c of the elastic fixing band 6 and/or asliding surface of the coupling FIG. 7 with fluorine type resin or tocoat with lubricant.

By thus configuring a tire, the elastic fixing band 6 automaticallyabsorbs the external force which may generate a buckling phenomenon orthe like, whereby a fatigue life of the elastic fixing band 6 can beprolonged, and stable attachment of the band-shaped sound absorbingmaterial 5 to the inner surface of the tread becomes possible.Incidentally, a situation shown in FIG. 11 indicates a situation wherebuckling occurs at a ground-contacting portion Q where the tire contacta ground surface G because the circumferential length of the elasticfixing band 6 incorporated in the tire is fixed constantly. Thisbuckling has conventionally brought about such problems that attachmentof the band-shaped sound absorbing material 5 becomes unstable, and thata fatigue life of the elastic fixing band 6 is shortened. However, inthe present invention as described above, if a tire has an elasticfixing band provided with the stretching mechanism which automaticallyadjusts the circumferential length of the elastic fixing band, suchproblems can be reduced.

Note that, in the abovementioned example, the case shown as an exampleis such that the band-shaped sound absorbing material 5 is attached bypressure to the inner surface of the tread portion by the elastic fixingband 6 from the outer periphery of the band-shaped sound absorbingmaterial 5. However, a positional relation in a radial direction of thetire between the elastic fixing band 6 and the band-shaped soundabsorbing material 5 is not limited to this case, and the band-shapedsound absorbing material 5 may be attached by pressure to the innersurface of the tread portion by the elastic fixing band 6 from the innerperiphery of the band-shaped sound absorbing material 5. Additionally,means for bonding the band-shaped sound absorbing material 5 with theelastic fixing band 6 may be determined by a kind and a shape of theband-shaped sound absorbing material 5, and is not particularly limited.However, it is possible to adopt bonding by a bond or by other couplingmeans.

EXAMPLES

Pneumatic tires with a tire size of 205/65R15 were prepared respectivelyas: a conventional tire (Conventional Example) where nothing wasattached in a cavity portion thereof and a tire of the present invention(Example) and comparative tires (Comparative Examples 1 and 2)respectively having sound absorbing materials attached in cavityportions thereof all around entire circumferences on inner surfaces oftread portions thereof as shown in FIG. 2 a, the sound absorbingmaterials having apparent densities defined in JIS K6400 made differentas shown in Table 1. Note that a width and a thickness of the soundabsorbing materials were commonly set to 150 mm and 40 mm, respectively.

Test tires of each of the Examples were mounted onto wheels of a rimsize of 15×6½ JJ respectively, and an air pressure thereof was set at220 kPa, and then were installed to a passenger automobile having adisplacement of 2500 cc. Then, a microphone was installed at a positioncorresponding to an ear of a driver on a window side in a driver's seatinside a car cabin, and noise in a car cabin at frequencies of 200 to250 Hz was measured when the automobile was run on a rough road surfacewith a speed of 50 km/h. Results of the measurement were averaged, andthe obtained averages were converted into index numbers with the averageof the conventional tire being set as 100, and are also shown inTable 1. A smaller value indicates that the noise is reduced.

TABLE 1 Conventional Comparative Comparative Example Example Example 1Example 2 Apparent density — 30  5 80 (kg/m³) Noise inside car 100 92100 99 cabin at frequencies of 200 to 250 Hz

From Table 1, it can be found that compared to the conventional tires,the tire of the present invention is reduced in cavity resonance noiseat the frequencies of 200 to 250 Hz.

INDUSTRIAL APPLICABILITY

The low noise pneumatic tire of the present invention can be used in thetire industry, and by extension can be effectively utilized in theautomobile industry as an instrument for realizing an automobile onwhich low noise pneumatic tires are mounted.

1. A low noise pneumatic tire, wherein a band-shaped sound absorbingmaterial formed of a porous material whose apparent density defined inJIS K6400 is in a range of 10 to 70 kg/m3 is attached to the innersurface of a tread by use of an elastic fixing band, wherein the elasticfixing band is arranged in an annular form along an inner peripheralsurface of the band-shaped sound absorbing material and is retained onthe inner surface of the tread under pressure through the elastic forceof the elastic fixing band.
 2. The low noise pneumatic tire according toclaim 1, wherein the band-shaped sound absorbing material is fixed allaround the entire circumference on the inner surface of the tread by useof the elastic fixing band.
 3. The low noise pneumatic tire according toclaim 1, wherein an irregular surface having step heights of 20 mm orless is formed on the inner peripheral surface of the band-shaped soundabsorbing material.
 4. The low noise pneumatic tire according to claim1, wherein a second porous material whose sound absorption coefficientdefined in JIS A1405 at a frequency of 200 Hz is 10% or more, is layeredon a cavity-facing surface of the band-shaped sound absorbing material.5. The low noise pneumatic tire according to claim 4, wherein theband-shaped sound absorbing material has a thickness in a range of 5 to45 mm, and the second porous material has a flat surface and has athickness in a range of 5 to 45 mm.
 6. The low noise pneumatic tireaccording to claim 4, wherein an irregularity having step heights of 20mm or less is formed on a surface of the second porous material.
 7. Thelow noise pneumatic tire according to claim 6, wherein the band-shapedsound absorbing material has a thickness in a range of 5 to 45 mm, andthe second porous material has a thickness in a range of 5 to 45 mm. 8.The low noise pneumatic tire according to claim 1, wherein a porousmaterial whose sound absorption coefficient defined in JIS A1405 at afrequency of 200 Hz is 10% or more, is layered on both inner and outersurfaces of the band-shaped sound absorbing material.
 9. A low noisepneumatic tire, wherein a band-shaped sound absorbing material formed ofa porous material whose apparent density defined in JIS K6400 is in arange of 10 to 70 kg/m3 is attached to the inner surface of a tread byuse of an elastic fixing band, wherein the elastic fixing band has astretching mechanism, which automatically adjusts a circumferentiallength of the elastic fixing band, in at least one location on thecircumference of the elastic fixing band.
 10. The low noise pneumatictire according to claim 9, wherein the stretching mechanism is formed ofan elastic spring mechanism.
 11. The low noise pneumatic tire accordingto claim 9, wherein the stretching mechanism is formed by coupling bothends of the elastic fixing band with each other in a manner that theelastic fixing band can slide.
 12. A low noise pneumatic tire, wherein aband-shaped sound absorbing material formed of a porous material whoseapparent density defined in JIS K6400 is in a range of 10 to 70 kg/m3 isattached to the inner surface of a tread by use of an elastic fixingband, wherein the elastic fixing band is fixed by a bond along an outerperipheral surface of the band-shaped sound absorbing material and isretained on the inner surface of the tread under pressure through theelastic force of the elastic fixing band.
 13. The low noise pneumatictire according to claim 12, wherein the band-shaped sound absorbingmaterial is fixed all around the entire circumference on the innersurface of the tread by use of the elastic fixing band.
 14. The lownoise pneumatic tire according to claim 12, wherein an irregular surfacehaving step heights of 20 mm or less is formed on the inner peripheralsurface of the band-shaped sound absorbing material.
 15. The low noisepneumatic tire according to claim 12, wherein a second porous materialwhose sound absorption coefficient defined in JIS A1405 at a frequencyof 200 Hz is 10% or more, is layered on a cavity-facing surface of theband-shaped sound absorbing material.
 16. The low noise pneumatic tireaccording to claim 15, wherein the band-shaped sound absorbing materialhas a thickness in a range of 5 to 45 mm, and the second porous materialhas a flat surface and has a thickness in a range of 5 to 45 mm.
 17. Thelow noise pneumatic tire according to claim 15, wherein an irregularityhaving step heights of 20 mm or less is formed on a surface of thesecond porous material.
 18. The low noise pneumatic tire according toclaim 17, wherein the band-shaped sound absorbing material has athickness in a range of 5 to 45 mm, and the second porous material has athickness in a range of 5 to 45 mm.
 19. The low noise pneumatic tireaccording to claim 12, wherein a porous material whose sound absorptioncoefficient defined in JIS A1405 at a frequency of 200 Hz is 10% ormore, is layered on both inner and outer surfaces of the band-shapedsound absorbing material.